Adaptive matched filters for contrast imaging
Résumé
The ultrasound (US) contrast imaging is a promising technique. Currently the scientific community of this field seeks US excitations which should make possible the optimization of the acoustic contrast. Two matched filters (MF) techniques are used to improve the image contrast. The first technique is an adaptive MF technique and the second is a RLS technique derived from identification theory. The system proposed is a close loop system which optimizes the power backscattered by microbubbles. After having transmit a first signal, the backscattered power is optimized by transmitting the matched filtered signal at each iteration. This process is iterated until convergence. Simulations are carried out for encapsulated microbubbles of 2 microns by considering the modified Rayleigh-Plesset equation for a 2.25 MHz transmitted frequency and for various pressure levels (20 kPa up to 420 kPa). In vitro, experiments are carried out by using two transducers a transducers which were placed perpendicularly. The signal was transmitted through a 2.25 MHz transducer. Responses of a 1/2000 diluted solution of SonoVue were measured by a 3.5 MHz transducer. Each experiment has been realized with three pressure levels (127, 244 and 370 kPa). We show through simulations and through in vitro experiments that our adaptive imaging technique gives in case of simulations a gain which can reach 12 dB compared to the traditional technique and for in vitro experiments, the MF gives a gain which can reach 4.5 dB whereas the MF derived from identification theory can reach 6 dB.
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